This invention relates to electrical connecting devices, and particularly to an electrical adapter plug which may be inserted into the sockets or receptacles of automotive cigarette lighter assemblies so that various low voltage loads may be operated by the electrical system of the vehicle.
In recent years, a great variety of electrical appliances have become available for operation by the low voltage, direct-current power of the electrical systems of cars, power boats, and campers. The appliance is generally interconnected to the electrical system of the vehicle by use of an adapter plug or connector which is inserted into the cigarette lighter socket or receptacle. Electrical appliances and accessories which can be operated from a vehicle electrical system vary widely and include portable television sets, tape recorders, trouble lights, window defrosters, electric shavers, electric toothbrushes, can openers, food mixers, and the like.
Such prior art devices useful for electrical connection with cigarette lighter receptacles include Focosi U.S. Pat. No. 2,954,544, Schwartz U.S. Pat. No. 3099,505, Busch et al. U.S. Pat. No. 3,377,610 and Busch U.S. Pat. No. 3,865,463.
In general, existing adapter plug designs each have one or two spring contacts mating with a receptacle sleeve. If there are two contacts, they are angularly spaced to project from the periphery of an adapter plug body at an angle of 180.degree.. Accordingly, the vector sum of the mechanical forces of two contacts within the sleeve are in-line or 180.degree. opposing and there is zero force on the body of the adapter plug to position it against the receptacle surface. Thus the adapter plug is able to pivot on the in-line contact points within the receptacle. When the adapter plug is free to pivot more, it can loosen and eventually lose electrical contact when subject to vibration or shock.